The present invention relates to a diagnosing apparatus and method for diagnosing the presence or absence of (wire) breakage of electromagnetic coil means applicable to a breakage diagnosis for a stepping motor.
A Japanese Patent Application First Publication No. Showa 60-215174 exemplifies a duty ratio controlled solenoid which drives an engine idling revolution speed control valve (ISC valve) disposed within an auxiliary air passage bypassing an intake air passage (including a throttle valve) in response to an input duty ratio varied pulse signal (hereinafter, also called a pulsewidth modulated signal) so as to derive an operating variable in proportion to a rate of an ON time duration (a duration of time during which the duty ratio varied pulse signal indicates a predetermined high level) to a period of the duty ratio varied signal, e.g., 6.4 ms.
In a case where the duty ratio controlled solenoid is used in such a situation as descried above, it is necessary to speedily detect a presence or absence in a breakage in the duty ratio controlled solenoid and to take a countermeasure against the detected breakage of the solenoid since it becomes difficult to perform a desired control with the breakage in the solenoid occurred.
Therefore, in the above-identified Japanese Patent Application First Publication, a current detecting circuit which detects an average value of a current flowing through the solenoid is installed so that the presence or absence in the breakage is detected on the basis of the average value of the current flowing through the solenoid.
However, since an expensive current monitor circuit is needed as the current detecting circuit, a cost of manufacturing the diagnosing apparatus becomes high. In addition, when the ON time duration of the duty ratio varied pulse signal is 0%, the current value gives zero irrespective of an absence or presence in the breakage of the solenoid so that the diagnosis whether the breakage in the solenoid occurs cannot completely be carried out.
In addition, a Japanese Patent Application Second (examined) Publication No. Heisei 2-63098 exemplifies stepping motors, one of which drives a purge control valve installed within a purge passage in order to purge a vaporized fuel from a canister on which the vaporized fuel from a fuel tank is adsorbed onto an intake air passage or the other of which drives the engine idling speed control valve (ISC valve) installed within the auxiliary air passage bypassing the intake air passage (throttle valve).
Such a stepping motor as described above is provided with a plurality of exciting coils on a stator, each exciting coil being excited (energized) in response to the predetermined high level of the duty ratio varied pulse signal having a constant duty ratio control period and being deenergized in response the predetermined low level of the input duty ratio varied signal in accordance with a predetermined sequential pattern of the exciting coil's excitation and deenergization (current interruption) so that the rotor has varied its angular position by one stepped number of time.
At any rate, in a latter case where the stepping motor is used in such situations as described above (engine idling speed control valve and purge control valve), it becomes difficult to perform a desired control when a (wire) breakage in at least one of the exciting coils of the stator occurs. It is necessary to speedily detect the breakage therein and to take a necessary countermeasure against the occurrence of the breakage. A checking signal circuit may be installed for each exciting coil which provides a checking pulse having a particular (logical) level only when no breakage in at least one exciting coil occurs with the input duty ratio varied pulse signal at either the predetermined high level or low level and the presence or absence in breakage of at least one exciting coil may be diagnosed according to the contents of the checking signals from the respective checking signal circuits. However, to carry out this diagnosis, it is necessary to determine whether the corresponding one of the checking signals is appropriate for the power supplied state of each exciting coil (ON time duration (predetermined high level) or OFF time duration (predetermined low level). In a case where the excitation and deenergization of each exciting coil of the stepping motor is carried out by a main CPU and the checking signals are provided for another sub CPU, it may be difficult for the sub CPU to detect the states of the input pulse duty ratio varied signal. Therefore, the diagnosis for tile breakage in such exciting coils as described above may not carried out.